#include<stdio.h>
int main()
{
	int a;
	float sum1=0.0,sum2=0.0;
	for (a = 1; a <= 100; a++)
	{
		if (a % 2 == 0)
		{
			sum1=sum1- (1.0f/a);
		}
		else
			sum2 = sum2+(1.0f/a);
	}
	printf("%f\n", sum1+sum2);

	return 0;
}